The invention discloses a modification method of a cerium-tin compound oxide coated lithium-rich manganese-based positive material. The body of the material is a lithium-rich manganese-based positivematerial, and the surface coated substance of the material is a cerium-tin compound oxide material containing rich oxygen defects. The modification method comprises the following preparation steps: (1) dispersing the lithium-rich manganese-based positive material into a secondary water solvent, and forming a uniform mixed solution through ultrasonic oscillation to be marked as an A solution; (2) dispersing a metal salt containing Sn and Ce elements into the secondary water solvent, adding an alkaline source to adjust the pH of the solution to be 12, and marking the solution to be a B solution;(3) after uniformly mixing the A solution and the B solution, putting the mixture into water at the temperature of 140 to 220 DEG C inside a reaction still for heat treatment for 12 to 36 h, and washing, filtering and drying to obtain a precursor material; and (4) after sufficiently grinding the precursor material, carrying out calcinations at the temperature of 450 to 650 DEG C for 3 to 10 h, and cooling to room temperature so as to obtain the cerium-tin compound oxide coated lithium-rich manganese-based positive material. According to the method, the surface coating for the lithium-rich manganese-based positive material is realized through hydro-thermal treatment, the preparation technology is simple, and the obtained material is high in degree of crystallinity, high in capacity and good in rate capability.